Your question is a loaded one. I'll try to point out some things you may want to take into consideration.
Discus are more expensive because they require a little more time and effort to raise than other tropical fish. It also depends on the color type. Some discus are more common (pigeon bloods, red turquoise, snakeskins) while others are more scarce (albinos). Sometimes there are many 'grades' of fish per spawn. This means that certain discus, like leopards and other spotted types, may produce several different variations of fry. The more intricate and fully spotted a fish is, the more money it's going to cost you... compared to its less spotted siblings.
Now, the next question would be about the pair you mentioned. There are a few things to consider about pairs. Are they a mated pair? This means they have successfully spawned and hatched eggs into fry. Mated pairs usually fetch a higher price because they are confirmed male and female. Mated pairs also tend to be expensive because it's instant gratification -- no raising juveniles to pair off, no waiting on the fish to start spawning. However, just because discus are a mated pair does not mean they will spawn for you. Unless your conditions are right and the fish are happy, there's a chance they'll never raise fry once they've been sold to you.
If the fish in question AREN'T a mated pair, but just two discus, I don't think they should be that price... not unless there's something special about them. Without pictures, it is impossible to assume what sort of discus this person is describing. Pigeon bloods can be spotted, but then so can leopards and all the leopard variants... and those are not pigeon-based fish.
The last question to ask yourself is, why do you want a pair? If you are new to discus, I would suggest getting some young fish and raising them up to learn about them first before I jumped into trying to breed them. Discus are not like other fish. They require more specialized care in general.
Ryan